Causes of red eye?

[machineman9]

I understand the main concept behind red eye... Flashes going too quickly, the eye can't keep up and the light is reflected back off the rear of the eye.

I am just wondering what, in a physical sense, can make red eye happen more.

What I mean is, I am an absolute horror for it... Take a photo and I will have 2 really red eyes. Take the same picture of a lot of people I know and they will keep the colour in their eyes much better.

So could someone explain how exactly people such as myself are more prone to it? I've read on how to reduce it and what is the cause of it - but only the general cause.


Cheers

[C]

Sounds like a question for a physicist.

I shall now leave the thread!

[skoker]

http://forums.cnet.com/5208-7593_102-0. ... 01&start=0
Its the retina reflecting light.

[machineman9]

Yeah, I understand that bit, I am just wondering why some people are more prone to it than others.

[BAW0343]

Bigger shiner retina?

[The Ruptured Duck]

My theory:  Some people have a tendancy to look at the camera more than others.  If someone is looking directly at the flash unit, the red eye will be worse than someone who is looking slightly away from it.

Does that make sense? :-?

[machineman9]

Yeah that does make sense... Goes with the theory on why it occurs and how to prevent it (change where the flash is, etc)

But what if two people do the exact same thing, look directly at the same place with the same distance from flash. Why then would some people get red eye much worse than others? Just how well their pupils contract?

[Fozzer]

I occasionally suffer from "Red Eye"....

...but I suspect its due to peering through semi-closed curtains, and a draughty open window, at next-door neighbour's delightful Daughter, sunbathing, semi-naked, in the back Garden... ....?

F.... ... ... ...!

...must spend more time reading the concise works of William Shakespeare?... ... ... ... ...!

[machineman9]

Just don't get caught 'red handed' with your leisure activities.

[beaky]

I'll play scientist for a minute...
What color are your eyes? If the irises are very light, perhaps more light is getting out of your eyes? Also, you just might be better-oxygenated. If we were to dissect one of your eyes, maybe we'd see that your retina is pinker and healtheir than most other people. Or maybe your irises are slow to contract or something.

I also like Duck's theory- with such a small aperture as the human pupil, a small difference in angle would have a big effect, I think.

[Steve M]

Got this off the web.
"While the light is inside our eye, it travels through many tiny blood vessels that are present to keep the eye alive. This is how the light gets its red color.

Of course, it takes a very powerful light to travel through these blood vessels, and return with enough intensity to be visible. If you shine a torch in someone's eye, it does not appear red for example. It is only the powerful flash bulb that makes this effect so visible."

Some people may have more capilaries or larger vessels than others. then again some cameras may flash brighter than others.

[expat]

Causes of red eye...................I am surprised, no jokes about smoking illegal and depending on your worldly location legal substances

[machineman9]

I'll play scientist for a minute...
What color are your eyes? If the irises are very light, perhaps more light is getting out of your eyes? Also, you just might be better-oxygenated. If we were to dissect one of your eyes, maybe we'd see that your retina is pinker and healtheir than most other people. Or maybe your irises are slow to contract or something.

I also like Duck's theory- with such a small aperture as the human pupil, a small difference in angle would have a big effect, I think.

Greenyish eyes I have. I didn't know colour of eyes could effect it. Learn something new everyday lol.

[skoker]

My biology teacher siad that it can also depend on the amount of lighting prior to the flash..  This is because the retna size will cause more light to enter the eye and cause red eye.

Basicly If you take a picture in a well lighted room the effects of red eyes will greatly decrease.

Or you could wear sunglasses 8-)

[machineman9]

Yeah defo. Dark room will cause much more red eye than daylight room because the change in light intensity will be much greater.

With my sunglasses, you would see the camera lol. Reflectors... Lovely!